The invention described herein may be manufactured, used, imported, sold, and licensed by or for the Government of the United States of America without the payment to us of any royalty thereon.
1. Field of the Invention
The present invention relates in general to the field of detecting and locating bar codes, and more specifically to detecting and locating the position of a postnet type barcode with an omnidirectional location orientation.
2. Description of the Prior Art
Bar codes were introduced over twenty years ago and their use has spread from supermarkets to department stores, warehouses, factory floors, the military, health and insurance industries. They are one of the simplest printed patterns that can be reliably recognized by a computer. A typical bar code consists of a sequence of parallel solid lines or bars of varying width and spacing. The alternating light and dark areas defined by the bars and the spaces between the bars represent a digital code that serves to identify the content of the bar code symbol. After being read, the digital code is directly translated to a sequence of alphanumeric characters and, then by means of a data base, the digital code may be further translated to the common language description of the item bearing the object bar code label along with other pertinent data such as the current price of the item.
A bar code reader includes a scanner and a decoder. A scanner is the device that produces a signal representing the bars and spaces of a bar code. A decoder then converts the signal so that a computer will understand the signal. The light sources used in scanners are LED (Light Emitting Diode), CCD (Charge Coupled Device) and lasers in manufacturing and warehousing applications. A scanner produces a well-defined beam of light that is scanned across a bar code symbol by means such as an oscillating galvanometer mirror or a rotating polygon. Scattered light from the symbol is collected by an optical system and is incident on a photodetector in the scanner. The photodetector converts the light into a time-varying analog signal that is an electrical representation of the physical bar and space widths. Subsequent circuits convert this signal to a logic level pattern whose analog timing represents the bar code symbol. This pattern is sent to a microcomputer to determine the characters in the message represented by the symbol.
Several types of bar codes have been prevalently utilized in the commerce and industry. The most common one is the one-dimensional bar code, or 1-D bar code. 1-D bar codes encode information along one dimension with intervals of alternating diffuse reflectivity, usually of black and white color. Each interval is a rectangle whose vertical dimension, or height, carries no information but rather facilitates scanning. Usually the codes use a combination of bar/space ratio, the ratio of bar/space width to the narrowest bar/space width, to represent different information. FIG. 1 shows an example of a prior art Code 39 bar code with two different widths for the bar and the space. In the bar code system, a bar is defined as the element type with the lower reflectance, usually black, and a space is the element type with higher reflectance, usually white. Obviously, a higher bar allows more various scanning directions, and however, occupies more available space.
During the later 1980s and early 1990s two dimensional bar codes or 2-D symbols have been developed for automatic identification. A 2-D bar code contains significantly more data than a 1-D bar code. Many 2-D bar codes can carry as many as 2,000 characters of data in a single symbol as compared to a 1-D bar code capacity of 15 to 22 characters. Most 2-D bar codes have error correction; that is, mathematical formulas are embedded into the code that will reconstruct any missing portion of the symbol and recreate the missing data. This allows the symbol to be easily used in environments where symbol damage is likely.
FIGS. 2A-2C depict three 2-D bar code examples. FIG. 2A shows the Vericode type 2-D bar code used for individual part tracking to identify unique parts in an automotive assembly and contains a unique identifier number and other pertinent information applicable to the tracking process. FIG. 2B shows the PDF 417 bar code that can contain quality test data and a tracking sheet to define needed parts, processes and fabrication requirements. The FIG. 2C Maxicode is used for high speed sorting, routing and tracking of goods.
The following patent references provide useful background information:
Willsie, U.S. Pat. No.: 5,120,940 xe2x80x9cDetection of Barcodes in Binary Images with Arbitrary Orientation,xe2x80x9d issued on June 91-D describes 1-D bar code recognition;
Chandler, et al., U.S. Pat. No. 5,155,343 xe2x80x9cOmnidirectional Bar Code Reader with Method and Apparatus for Detection and Scanning A Bar Code Symbol,xe2x80x9d issued on Oct. 13, 1992 describes a 1-D bar code recognition technique;
Fardeau et al., U.S. Pat. No. 5,155,344 xe2x80x9cMethod and Device for Reading a Bar Code of Variable Orientation on a Substantially Motionless Medium,xe2x80x9d issued on Oct. 13, 1992 describes 1-D indexation bar code; and
Van Tyne et al., U.S. Pat. No. 5,073,954 entitled xe2x80x9cBar Code Location And Recognition Processing System,xe2x80x9d issued on Dec. 17, 1991 describes recognition of a horizontal postnet bar code. The present invention discloses and claims methods and systems for detection of the omnidirectional located postnet barcode.
The postnet bar code is very useful for mail delivery. The postnet bar code, often called the one and a half dimension (1.5 D) barcode, has long and short bars representing a set of binary data that can be decoded to the zip code portion of an address. Unlike the 1-D and 2-D bar codes, the postnet long and short bars each have different heights, and the postnet bar code maintains the same bar width and interval between two consecutive bars. FIG. 3A shows the format of typical postnet bar code 10 having a width, w. FIG. 3B is an exploded side view of postnet bar code 10 depicting a long bar 11 and short bars 12 and 13, along with representative dimensions. The size relationship between the width of postnet bar code 10 and the heights for long bar 11 and short bars 12 and 13 limits possible variations of scanning direction, and requires high accuracy for automatic recognition of postnet bar codes. The inherent size relationships in postnet bar codes, and hence, the requirement for high accuracy in automatic character recognition, has caused a number of problems, limitations and shortcomings. These problems, particularly the lack of freedom for scanning direction, have created a long-standing need for more versatility in character recognition, called recognition robustness, and a larger angle of rotation angle. The present invention overcomes and resolves the long-standing problems, shortcomings, limitations and difficulties associated with bar height, lack of scanning direction and high accuracy by providing heretofore unavailable methods and apparatus for precision detection of postnet bar codes with an omnidirectional orientation and arbitrary placement on the object.
It is one object of the present invention to provide a method for automatic detection of the position of postnet barcode omnidirectionally located in a 2-D digital image.
It is one object of the present invention to provide an apparatus for automatic detection of the position of postnet barcode omnidirectionally located in a 2-D digital image.
To attain these and other advantages and objects, the present invention provides for methods for rapid and precise detecting of an omnidirectional postnet bar code on an object by digital signal processing, comprising the steps of image processing, image recognition, providing a down-sampled image, correlating an image with matched filtering, forming a multi-resolution image structure, generating correlation results from the match-filtering step, detecting a position and an orientation of the postnet bar code location by matching the postnet bar code location with a verification result, without suffering from any of the long-standing problems, shortcomings and limitations associated with scanning direction constraints and the high accuracy requirement. One possible embodiment of the methods of the present invention is a method of mail sorting that automatically sort magazines on a moving conveyor belt into different slots according to the address information contained in the postnet bar code.
The present invention also contemplates an omnidirectional postnet bar code detecting system that may be embodied in a computer-implemented apparatus or a computer-readable storage medium.